1. Field of the Invention
The present invention relates to an electrode for a nonaqueous electrolyte secondary battery and a method of manufacturing the same.
2. Description of Related Art
Japanese Patent Application Publication No. 2011-119092 (JP 2011-119092 A) discloses an electrode which contains active material particles having a hollow structure (hereinafter, referred to as “hollow active material particle”).
The hollow active material particles can hold an electrolytic solution in hollow portions thereof. As a result, in an electrode mixture layer containing the hollow active material particles, a reduction in the non-uniformity of the electrolytic solution distribution can be expected. However, in an electrode including the hollow active material particles, there is room for improvement in terms of the following points.
In general, an electrode for a nonaqueous electrolyte secondary battery is manufactured by applying a paste containing active material particles to a current collector foil. This paste is a dispersion in which active material particles, a binder, and the like are dispersed in a solvent. In the hollow active material particles, a solvent for a paste may penetrate into hollow portions thereof. For example, when a solvent having a high boiling point such as N-methyl-2-pyrrolidone (NMP) is used, even after a drying step of drying a paste, the solvent penetrating into the hollow portions may remain in the hollow portions without being completely volatilized. When a solvent remains in the hollow portions, the hollow portions cannot hold an electrolytic solution. Accordingly, the effects expected from the hollow active material particles may be reduced.
In order to promote the volatilization of a solvent, various countermeasures such as an increase in the hot air drying temperature or hot air flow rate of the drying step may be considered. However, in this case, large heat convection occurs during the drying of a solvent, which promotes the migration of a binder to the surface of a coating film. In an electrode mixture layer formed using the above-described method, the binder segregates in the surface thereof, which decreases reactivity on the surface of an electrode. Further, the amount of the binder is insufficient at an interface between the electrode mixture layer and a current collector foil, which decreases the peeling strength of the electrode mixture layer.